C++多重映射 cbegin()函数用于返回指向多重映射集合第一个元素的常量迭代器。
const_iterator cbegin() const noexcept; //since C++ 11
const_iterator 是指向常量内容的迭代器。
它返回一个指向multimap的第一个元素的const_iterator。
让我们看一下cbegin()函数的简单示例:
#include <iostream> #include <map> using namespace std; int main () { multimap<char,string> mymultimap; mymultimap = { {'a',"Java"}, {'b', "C++"}, {'b', "Python"}, {'a', "Android"} }; //show content: for (auto it = mymultimap.cbegin(); it != mymultimap.cend(); ++it) cout <<(*it).first << " => " << (*it).second << '\n'; return 0; }
输出:
a => Java a => Android b => C++ b => Python
在上面的示例中,cbegin()函数用于返回const_iterator,该const_iterator指向mymultimap多重映射中的第一个元素。
让我们看一个简单的示例,使用for-each循环遍历multimap:
#include <iostream> #include <map> #include <string> #include <iterator> #include <algorithm> using namespace std; int main() { multimap<string, int> m; m= { {"Room1", 100}, {"Room2", 200}, {"Room1", 300}, {"Room1", 100} }; // Iterate over a multimap using std::for_each and Lambda function for_each(m.cbegin(), m.cend(), [](pair<string, int> element){ // Accessing KEY from element string word = element.first; // Accessing VALUE from element. int count = element.second; cout<<word<<" = "<<count<<endl; }); return 0; }
输出:
Room1 = 100 Room1 = 300 Room1 = 100 Room2 = 200
在上面的示例中,我们使用STL算法std ::for-each迭代multimap。它将在每个multimap元素上进行迭代,并调用我们提供的回调。
让我们看一个简单的示例,使用while循环遍历multimap:
链接:https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-multimap-cbegin-function.html
来源:LearnFk无涯教程网
#include <iostream> #include <map> #include <string> int main() { using namespace std; multimap<int,string> mymultimap = { { 100, "Nikita"}, { 200, "Deep" }, { 300, "Priya" }, { 200, "Suman" }, { 400, "Aman" }}; multimap<int, string>::const_iterator it;//declare an iterator it = mymultimap.cbegin();//assign it to the start of the multimap while (it != mymultimap.cend())//while it hasn't reach the end { cout << it->first << " = " << it->second << "\n"; // print the value of the element it points to ++it;//and iterate to the next element } cout << endl; }
输出:
100 = Nikita 200 = Deep 200 = Suman 300 = Priya 400 = Aman
在上面的示例中,cbegin()函数用于返回const_iterator,该const_iterator指向mymultimap多重映射中的第一个元素。
让我们看另一个简单的例子:
#include <map> #include <iostream> int main() { using namespace std; multimap <int, int> m1; multimap <int, int> ::iterator m1_Iter; multimap <int, int> ::const_iterator m1_cIter; typedef pair <int, int> Int_Pair; m1.insert ( Int_Pair ( 0, 0 ) ); m1.insert ( Int_Pair ( 1, 1 ) ); m1.insert ( Int_Pair ( 2, 4 ) ); m1_cIter = m1.cbegin (); cout << "The first element of m1 is " << m1_cIter -> first << endl; m1_Iter = m1.begin (); m1.erase ( m1_Iter ); //The following 2 lines would err as the iterator is const //m1_cIter = m1.begin (); //m1.erase ( m1_cIter ); m1_cIter = m1.cbegin(); cout << "First element of m1 is now " << m1_cIter -> first << endl; }
输出:
The first element of m1 is 0 First element of m1 is now 1
在上面的示例中,cbegin()函数用于返回const_iterator,该const_iterator指向mymultimap多重映射中的第一个元素。
祝学习愉快!(内容编辑有误?请选中要编辑内容 -> 右键 -> 修改 -> 提交!)